This invention pertains to mobile storage systems of the type wherein one or more storage units are movable on tracks to create an access aisle between two of the units and to establish the others in close side-by-side relationship to thereby minimize the amount of floor space required.
Some examples of movable storage units are library bookshelves, file cabinets, film storage files and racks used in warehouses and industry to store parts and finished and unfinished goods. Typically, the storage units are mounted on wheeled carriages which run on tracks. Each carriage has at least one reversible electric motor for propelling it bidirectionally. Usually, at least one outermost storage unit is stationary and the other units are controlled to move toward and away from it to form an aisle somewhere in the group of units.
The present invention achieves several improvements over a prior art system wherein commands by the user for opening an aisle are not initiated in the usual way by pressing pushbuttons but, instead, by causing a leash that normally spans between a closed aisle to become unspanned and thereby provide the move command signal. In typical prior art leash control systems devices called holders are mounted on the front face of each upstanding mobile shelf unit. These holders are essentially electrical sockets. A flexible and self-coiling electric cord or leash is electrically connected to contacts in one socket or holder and another end of the leash has an electric plug attached to it. The plug is otherwise known as a card which is insertable in a holder to make selective electrical connections.
In the prior art systems and in the improved control system described herein, when the user desires to open an aisle between two adjacent mobile shelving units, or between a mobile and a stationary unit, it is necessary for all aisles that are not intended to be accessed to be spanned by the self-coiling and stretchable leash. In other words, the leash attached at one end to a holder on one mobile unit must be placed across any aisle that is not to be accessed and the card at the other end of the leash must be plugged into the holder or socket on the next consecutive unit. The aisle that is to be accessed is chosen by unplugging or removing a card from the holder on the unit on one side of the intended aisle and inserting the card in its own holder on the unit at the other side of the aisle. This results in production of a move command signal which causes the carriage motors to run and drive the mobile units to the left or right as required for opening the aisle. The units are driven until their limit switches are actuated which occurs a moment before the storage units abut each other for completely closing those aisles for which no access is desired.
Systems requiring manipulation of leashes to selectively initiate an aisle opening sequence have been adopted to a large extent for economic reasons. The electric controls and logic circuitry can be more simple and unsophisticated than some of the systems that require user actuation of pushbuttons or switches. The economy and simplicity is, however, achieved in the prior art at the expense of sacrificing some safety features and other desirable functional features as well. For instance, in prior art leash control systems if there is an obstruction such as a small box or part that might drop on the floor between storage units in a formerly open aisle before or during the time that the other units are shifting to open an aisle, the obstructing article can be impacted with the result that the system jams before all of the units can abut each other. At this time there may be very little space between the units for removing the obstruction. This requires driving the units encountering the obstruction away from each other to make the obstructing article accessible in a more widely opened aisle. Thus, prior art electric control systems are usually provided with a key operable switch which must be actuated by the user for coping with an obstruction to override the normal electric control logic and safety devices and set up conditions whereby the aisle containing the obstruction can be opened.
A method previously used to avoid damaging an obstructing object or person in storage unit systems that do not use leashes but use push button or other switches instead, is to equip the storage unit carriages with a sweep bar that sweeps along the floor and actuates a movement arresting safety switch when the bar strikes the object. In prior art systems, when the sweep bar is actuated the carriage is not only inhibited from moving toward the obstruction but the whole system is deactivated and the carriages cannot be moved away from the obstruction until some inconvenient measures are taken. For instance, the user has been compelled to operate a key switch or the like which causes overriding of all of the safety switches so that the mobile unit that has encountered the obstruction can be moved away from it. It is obviously undesirable to inhibit operation of the safety sweep switches.
Safety sweep bars operating drive motor deactivating circuits have been used in control systems where there are pushbutton switch stations on each movable carriage for issuing left and right movement commands to the carriages but, insofar as applicant is aware, no one has successfully used the safety sweep concept in combination with leash control.